Conventionally, there is known an LED illumination device in which the light emission centers of monochromic LED chips of three primary colors are aligned to obtain, e.g., white irradiation light. In this LED illumination device, a single red LED chip is placed at the center of a substrate, while a plurality of green LED chips and a plurality of blue LED chips are arranged so that the LED chips of the same blue or green color are symmetrical with respect to the center of the substrate (see, e.g., JP Utility Model 6-79165A).
In this LED illumination device, the red LED chip is arranged at the center of the substrate by taking into account a fact that the LED chips of different colors are used as light emission dots of a display device, which serves primarily as a planar light source, and by paying attention to the color mixing performance at the central portion of a light emission surface. Such arrangement of the red LED chip helps prevent occurrence of chromaticity variations in the red color which is most sensitive to the eyes of a man and assists in reducing color heterogeneity in the high luminance region of a light emission surface.
However, in case where an LED lamp of the afore-mentioned LED illumination device is used as a spotlight for irradiating a wall surface or the like, a hue of two colors, i.e., a green color and a blue color, is generated in the low luminance region of a peripheral portion of an irradiation pattern. Therefore, chromaticity variations are likely to occur.